<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <div id="app">
    <div :style="{width:100*3+'px',height:200+'px',backgroundColor:'red'}"></div>
    <div :style="{width:100*3+'px',height:200+'px',backgroundColor:isRed?'red':'blue'}"></div>
  </div>
  <script src="./vue.js"></script>
  <script>
    const vm = new Vue({
      el: '#app',
      data:{
        isRed:false
      }
    })
  </script>
</body>
</html>